Diplodia canker

Diplodia canker, caused by the fungus Diplodia mutila, is a destructive plant disease that affects a wide variety of woody hosts. As a primary or opportunistic pathogen, it infects the host through bark injuries, pruning wounds, or natural openings. Once inside the host tissues, the fungus colonizes the cambium, obstructing the transport of water and nutrients throughout the tree.

The host range of Diplodia mutila includes many deciduous trees, fruit crops like apples and pears, as well as various ornamental species. Trees that are already experiencing stress due to drought, poor soil nutrition, or environmental extremes are significantly more susceptible to successful infection and subsequent colonisation by this fungus.

Symptoms of the infection typically manifest as sunken, discolored lesions on the bark that eventually enlarge and form perennial cankers. Within the dead bark, small, pimple-like structures called pycnidia develop, which serve as the reproductive units for the pathogen. In advanced stages, the canopy may show progressive wilting, leaf chlorosis, and branch dieback leading to the decline of the tree.

The spread of the disease is heavily dependent on moisture. Rain splash and high humidity facilitate the dispersal of spores from the pycnidia to healthy parts of the tree or neighboring plants. The fungus thrives in warm, temperate climates and can persist for extended periods in dead organic matter, making it a difficult pathogen to eradicate once it is established in an orchard or forest.

Management of this fungal disease requires an integrated strategy to minimize inoculum and bolster tree vigor. Key steps include the removal and destruction of infected branches to reduce spore pressure, ensuring tools are disinfected to prevent spread, and applying protective fungicides during the dormant season or early bud break. Long-term tree health is best maintained through proper irrigation, fertilization, and protecting the bark from mechanical and environmental injury.